We can translate the equation
sinv=−21
to the problem of finding those angles in the unit circle which have a y-coordinate of
−21. If we compare this with the problem that we had in exercise a, where we looked for angles which satisfied
sinv=+21, then the situation is the same, except that the angles now lie under, rather than above, the
x
-axis, due to reflectional symmetry.
Angle
2−6=611
Angle
+6=67
The two angles which satisfy
sinv=−21
lie in the third and fourth quadrants and are
v=2−6=611
and
v=+6=67
−